Polyurethane materials are synthesized by reacting polyisocyanates with polyols. In general, examples of polyols used include polyether polyols such as poly(ethylene oxide) and poly(propylene oxide), modified polyether polyols, polytetramethylene glycol, condensation polyester polyols produced by reacting dicarboxylic acids with diols, lactone-type polyester polyols produced by ring opening polymerization of ε-caprolactone or the like, and polycarbonate polyols. Polyurethane materials synthesized using these polyols exhibit insufficient weatherability, light resistance, heat resistance, hot water resistance, and hydrolysis resistance because they contain many heteroatoms in the main chains. In particular, in applications in which the polyurethane materials are in contact with water for a long period of time, since the polyurethane materials are easily hydrolyzed, insufficient durability gives rise to problems.
In order to overcome such problems, as polyol materials, vinyl polymers into which hydroxyl groups are introduced have been invented. Examples thereof include a polyol having polyisobutylene as the main chain (Japanese Unexamined Patent Application Publication No. 11-131325); a process for polymerizing styrene or butadiene using an initiator having hydroxyl groups (J. Polym. Sci., Part A1, 1971, Vol. 9, page 2029); a polymerization process in which hydroxyl group-containing dithiocarbamate or hydroxyl group-containing thiuram disulfide is used as an initiator or a chain transfer agent (Japanese Unexamined Patent Application Publication No. 61-271306); a polymerization process in which a disulfide having hydroxyl groups at both ends, a trisulfide having a hydroxyl group at each end, or the like, is used as a chain transfer agent (Japanese Unexamined Patent Application Publication No. 54-47782); processes for radically polymerizing vinyl monomers using polysulfide compounds having hydroxyl groups at both ends as chain transfer agents (Japanese Patent No. 2594402, Japanese Unexamined Patent Application Publication No. 6-211922, and Japanese Unexamined Patent Application Publication No. 5-262808); and a process in which a vinyl polymer having halogen atoms at both ends is produced by atom transfer radical polymerization using a metal complex as a catalyst, and the halogen atoms are converted into hydroxyl groups (Japanese Unexamined Patent Application Publication No. 2000-53723). Although the polyurethane polymers using these polyols have overcome some of the problems described above, a polyurethane polymer which is satisfactory in every aspect, e.g., physical properties, the range of usable monomers, ease of production, and cost, has not been produced yet.
Polyurethane elastic fibers are usually produced by wet spinning, dry spinning, melt spinning, or the like, and polymers constituting these fibers are linear block copolymers including hard segments which have high melting points and soft segments which have glass transition temperatures below room temperature and which are highly flexible. Since the soft segments are usually composed of polyether polyols, polyester polyols, polycarbonate polyols, or the like, the problems described above, in particular, poor light resistance and chlorine resistance, arise. With respect to light resistance, examples of problems include yellowing due to light, and loss of contraction and expansion properties and stretch and recovery properties. With respect to chlorine resistance, examples of problems include loss of contraction and expansion properties of clothing for swimming, such as swimwear, due to the use of chlorine as a bactericide at swimming pools; embrittlement of clothing, such as underwear, due to chlorine bleaches during washing; and embrittlement of clothing, such as swimwear and underwear, due to the presence of chlorine in tap water.
In order to improve chlorine resistance, some methods have been suggested, e.g., a method in which magnesium oxide or aluminum oxide is incorporated into polyurethane constituting fibers (Japanese Examined Patent Application Publication No. 61-35283), and a method in which zinc oxide is incorporated (Japanese Examined Patent Application Publication No. 60-43444). However, due to unsatisfactory solubility or dispersibility of these metal oxides in spinning solutions, uniformity is not achieved. Consequently, the resultant elastic fibers may become mottled, the metal oxides may adhere to spinnerets, and end breakage may easily occur, resulting in a decrease in productivity. Moreover, in the dyeing step, the metal oxides may be removed, and thereby satisfactory chlorine resistance is not exhibited.
In order to improve light resistance, some methods are known in which ultraviolet absorbers (such as benzotriazole-based, benzophenone-based, and salicylic acid-based ultraviolet absorbers) are added to polyurethane constituting fibers. However, in such methods, as in the chlorine resistance-improving methods described above, these ultraviolet absorbers have low solubility in spinning solutions and easily adhere to spinnerets, and end breakage easily occurs. Furthermore, the ultraviolet absorbers are expensive, thus being uneconomical.
On the other hand, polyurethane elastic fibers using polyester polyols or polycarbonate polyols can be produced by melt spinning. However, because of the presence of ester bonds in the main chains, they have insufficient hot water resistance, alkali resistance, and mildew resistance.
In order to overcome the problems described above, some methods have been suggested, e.g., the process in which polyisobutylene is used as the polyol for soft segments in polyurethane elastic fibers (Japanese Unexamined Patent Application Publication No. 11-131325) and a process in which a vinyl polymer synthesized by atom transfer radical polymerization is used (Japanese Unexamined Patent Application Publication No. 2000-72841). However, when polyisobutylene is used as a polyol, the strength is low because no hydrogen bonds are present in the polyol portion. When a vinyl polymer synthesized by atom transfer radical polymerization is used, complicated purification steps are required because a metal complex is used as a catalyst, resulting in an increase in production cost and a decrease in productivity.